Aerial system propulsion assembly and method of use

ABSTRACT

An aerial vehicle including a housing, an outrunner motor including a stator mechanically coupled to the housing and a rotor rotationally coupled to the stator, and a propeller removably coupled to the rotor, the propeller including a hub and a plurality of propeller blades. A rotor, a propeller including a hub and a propeller blade, a radial alignment mechanism, a rotational retention mechanism, and an axial retention mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/326,794, filed on 24 Apr. 2016, U.S. Provisional Application Ser.No. 62/326,795, filed on 24 Apr. 2016, and U.S. Provisional ApplicationSer. No. 62/412,408, filed on 25 Oct. 2016, all of which areincorporated in their entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the aerial system field, and morespecifically to a new and useful aerial system propulsion assembly andmethod of use.

BACKGROUND

Aerial system propellers can be awkward and/or difficult to install andremove, and typical propellers often operate with poor aerodynamicperformance. Thus, there is a need in the aerial system field to createan improved aerial system propulsion assembly and method for use.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a perspective view of an embodiment of the system;

FIG. 1B is a partial perspective view of a variation of the embodiment;

FIG. 2 is a perspective view of a first example of a propulsionassembly, in an unmated configuration;

FIG. 3 is a plan view of the first example, in a mated configuration;

FIG. 4A is a cross-sectional view taken along the line C-C in FIG. 3;

FIG. 4B is a detailed view of a region of FIG. 4A;

FIG. 5A is a detailed view of region I in FIG. 4A;

FIG. 5B is a detailed view of an axial retention mechanism of the firstexample, transitioning between the unmated and mated configurations;

FIG. 6 is a detailed view of region II in FIG. 4A;

FIG. 7A is a cross-sectional view taken along the line F-F in FIG. 3;

FIG. 7B is a plan view of the motor and a portion of the matingmechanisms of the first example;

FIG. 7C is a plan view of the propeller and a portion of the matingmechanisms of the first example;

FIG. 8A is a perspective view of a second example of the propulsionassembly, in a mated configuration;

FIG. 8B is a cross-sectional perspective view of the second example,transitioning between the unmated and mated configurations;

FIG. 9A is a perspective view of a portion of a third example of thepropulsion assembly;

FIG. 9B is a cross-sectional view of the third example, in a matedconfiguration;

FIG. 10A is a perspective view of a propeller of a fourth example of thepropulsion assembly;

FIG. 10B is a cross-sectional view of a propeller blade of the fourthexample;

FIG. 11 depicts the power loading curve of a specific example of thepropeller during aerial system hovering;

FIGS. 12A and 12B depict the twist angle and chord length, respectively,along the length of the specific example of the propeller;

FIG. 13 is a schematic representation of the method;

FIG. 14 is a schematic representation of a specific example of themethod;

FIG. 15 is a cross-sectional view of a second example of a propulsionassembly, in the mated configuration;

FIG. 16 is a perspective view of a first specific example of thepropeller of the second example;

FIG. 17 is a perspective view of a second specific example of thepropeller of the second example; and

FIGS. 18A-18C are perspective views of the second specific example ofthe propeller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the inventionis not intended to limit the invention to these preferred embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

1. Overview.

As shown in FIGS. 1A-1B, the aerial system 1 preferably includes ahousing 3 and one or more propulsion assemblies 2 (e.g., as described inU.S. application Ser. No. 15/349,749, filed on 11 Nov. 2016, which isincorporated in its entirety by this reference). However, the aerialsystem 1 can additionally or alternatively include any other suitableelements.

Each propulsion assembly 2 is preferably a motorized propeller assembly(e.g., the rotor described in U.S. application Ser. No. 15/349,749,filed on 11 Nov. 2016, which is incorporated in its entirety by thisreference). As shown in FIGS. 2 and 15, the propulsion assembly 2preferably includes a motor 100, a propeller 200, and one or more matingmechanisms. However, the propulsion assembly 2 can additionally oralternatively include any other suitable elements.

2. Benefits.

The aerial system 1 and method 400 can confer several benefits overconventional aerial systems 1 and methods of use. First, the propulsionassembly 2 can enable facile installation and removal of the propeller200 using few tools or no tools (e.g., manual removal). The propulsionassembly 2 can be configured to provide feedback (e.g., haptic feedback,acoustic feedback such as clicking, etc.) during the propellerinstallation process (e.g., mating the propeller 200 to the motor 100)and/or removal process (e.g., unmating the propeller 200 from the motor100), which can function to aid performance of the method 400 (e.g., byproviding confirmation of correct installation and/or removal). Thepropulsion assembly 2 can aid propeller installation by includingalignment features (e.g., elements of the mating mechanisms), which canhelp achieve and/or maintain alignment between the motor 100 andpropeller 200 during installation. Additionally or alternatively, thepropulsion assembly 2 can enable facile propeller installation by beingradially symmetric (or including elements with radial symmetry, such aselements of the mating mechanisms), which can allow propellerinstallation in a plurality of rotational alignments.

Second, during aerial system flight (and/or during other propulsionassembly operation), the force generated by the propeller 200 (e.g.,reaction force caused by air displaced by the propeller 200) can helpretain the propulsion assembly 2 in a mated configuration (e.g., keepthe propeller 200 mated to the motor 100). This retention force canfunction to counteract forces that otherwise might cause the propeller200 to become unmated from the motor 100 (e.g., centrifugal forcesexperienced during flight maneuvers). For example, the propeller 200 canbe arranged below (e.g., relative to a typical aerial systemorientation, relative to a gravity vector, etc.) the motor 100, and canbe mated to the motor 100 by an upward force and unmated by a downwardforce. In this example, when the propulsion assembly 2 is operated(e.g., to provide propulsion to maintain an aerial system hover orotherwise counteract gravitational forces, to perform flight maneuvers,etc.), the propeller 200 is retained against the motor 100 by a forcesubstantially opposing the unmating force direction (and substantiallyaligned with the mating force direction).

Third, the propulsion assembly 2 can be compatible with a plurality ofmating mechanisms, which can enable additional versatility. For example,the system can include a first propeller 200 configured to mate with themotor 100 using snap-fit mating mechanisms and a second propeller 200configured to mate with the motor 100 using screw-based matingmechanisms. In this example, the first and second propellers can beeasily swapped into and out of the system, despite their use ofdifferent mating mechanisms.

Fourth, the propeller 200 can operate with good aerodynamic performanceand/or generate little noise during operation. This benefit can beenabled by the design of the propeller blades 220. For example, thepropeller 200 can include blades 220 defining airfoils with largecamber, small thickness, high lift coefficient, and/or high lift-to-dragratio under low Reynolds number conditions. However, the aerial system 1and method 400 can additionally or alternatively confer any othersuitable benefits.

3. Aerial System.

3.1 Motor.

The motor 100 preferably functions to drive and/or control rotation ofthe propeller 200 and to mount the propeller 200 to the aerial systemhousing 3. The motor 100 preferably includes a stator 110 and a rotor120, and can additionally or alternatively include any other suitableelements.

The motor 100 preferably has a low profile (e.g., to facilitateattachment to and/or containment within the aerial system housing). Themotor 100 preferably has a high torque output, which can enable themotor 100 to directly drive the propeller 200 (e.g., without interveninggearing) in some embodiments; however, the motor 100 can have a lowtorque output, variable torque output, or any other suitable set ofoutput parameters. The motor 100 is preferably a DC electric motor, morepreferably a brushless DC electric motor, but can additionally oralternatively be powered by AC electricity, by internal combustion,and/or in any other suitable manner. The motor 100 is preferably anoutrunner motor, but can alternatively be a inrunner motor, ferritemotor, and/or any other suitable motor. The motor 100 preferablyincludes an electrical connector (e.g., connected to the stator 110),which can function to provide power to the motor 100 and/or to controlmotor operation. However, the motor can be otherwise powered and/orcontrolled.

The stator 110 can be mechanically coupled to the aerial system 1. Thestator 110 is preferably mechanically coupled to the aerial systemhousing, more preferably connected to and/or fixed with respect to thehousing or a portion of the housing (e.g., by one or more mechanicalfasteners). The stator 110 is preferably mounted to the housing fromabove (e.g., relative to a typical aerial system orientation, relativeto a gravity vector, etc.), such as by mounting an upper portion of thestator no to an upper portion of the housing (e.g., in systems in whichthe housing surrounds the propulsion assembly 2), which can enablemounting the propeller 200 to the stator no from below. However, thestator 110 can include any other suitable elements, and can be arrangedin any other suitable manner.

The rotor 120 is preferably rotationally coupled to the stator 110 abouta rotor axis 123. The rotor 120 can define a rotor body (e.g., a rotorbody defining and/or including a cylindrical body or body segment;polygonal prismatic body or body segment, such as one defining a regularpolygonal cross-section; rounded body such as a spherical, spheroidal,or hemispherical body; etc.). The rotor body preferably extends along anaxis (e.g., cylindrical body axis), more preferably the rotor axis 123,and can define a first end 121, a second end 122 (e.g., opposing thefirst end 121), and/or a rotor width such as a rotor diameter 124 (e.g.,as shown in FIGS. 4A and 7A).

However, the motor 100 can additionally or alternatively include anyother suitable elements in any suitable arrangement.

3.2 Propeller.

The propeller 200 can function to propel the aerial system 1 and/orcontrol aerial system flight. The propeller 200 preferably includes ahub 210 and one or more blades 220, and can additionally oralternatively include any other suitable elements (e.g., as shown inFIGS. 3 and 10A).

3.2.1 Hub.

The hub 210 can define a hub body (e.g., a hub body defining and/orincluding a cylindrical body or body segment; polygonal prismatic bodyor body segment, such as one defining a regular polygonal cross-section;rounded body such as a spherical, spheroidal, or hemispherical body;etc.). The hub body preferably extends along an axis (e.g., cylindricalbody axis), such as a hub axis 211. The hub body preferably defines avoid (e.g., cylindrical void; void complementary to the rotor body, suchthat the rotor body can be inserted into the void; etc.). The void candefine a void width such as a hub inner diameter 212.

The hub 210 is preferably configured to mate with the rotor 120 (e.g.,removably, permanently, etc.). In a first embodiment, one of the rotor120 and hub 210 (inner element) is configured to insert into the other(outer element). In this embodiment, a gap is preferably defined betweenthe rotor 120 and hub 210. The gap can function to decrease vibrationtransfer and/or amplification between the motor 10 o and propeller 200(e.g., thereby reducing audible noise generated during propulsionassembly operation). For example, a diameter (e.g., largest diameter) ofthe inner element can be less than an inner diameter of the outerelement, and the gap can be defined by the difference in diameters. Thegap can be greater and/or less than a threshold value, such as anabsolute distance (e.g., 10 mm, 5 mm, 2 mm, 1 mm, 0.5 mm, 0.2 mm, 0.1mm, etc.), a relative distance (e.g., a percentage of a rotor and/or hubdiameter, such as 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 10%, etc.), and/or anyother suitable value.

In this embodiment, the outer element preferably does not detach fromthe inner element in response to an applied torque (e.g., about an axisperpendicular to the rotor axis 123 and/or hub axis 211). Preferably,the inner element restricts removal of the outer element alongdirections that are not substantially aligned with the inner elementaxis. For example, the outer element can define an outer element endplane normal the outer element axis, the outer element end plane andinner element axis can define an intersection point, and a distance fromthe intersection point to a region of the inner element within the outerelement can be greater than half the outer element inner diameter (e.g.,such that the region of the inner element interferes with the outerelement during removal along a direction that is not substantiallyaligned with the inner element axis). In a specific example (e.g., asshown in FIG. 4B), the inner diameter of the outer element can be lessthan twice an inner element diagonal length (e.g., distance from theintersection point to an external region of the inner element within theouter element).

In a first variation of this embodiment, the rotor 120 is the innerelement and the hub 210 is the outer element. In this variation, therotor 120 is configured to be inserted into the hub 210 (e.g., rotorbody insertable into a void defined by the hub 210), and the rotordiameter 124 is less than a hub inner diameter 212 to accommodate suchinsertion (e.g., wherein the gap is defined by the difference betweenthe diameters). In this variation, the rotor 120 is preferably insertedinto the hub void (e.g., into an opening of the void at a hub end, suchas one defining a hub end plane normal to the hub axis 211) beginningwith the first end 121 (e.g., wherein the second end 122 is insertedfollowing the first end 121, wherein the second end 122 remains outsidethe void, etc.). In a second variation, the rotor 120 is the outerelement and the hub 210 is the inner element. In this variation, the hub210 is configured to be inserted into the rotor 120 (e.g., into a voiddefined by the rotor 120), and a hub outer diameter is less than a rotorinner diameter (e.g., defined by the void).

However, the rotor 120 can additionally or alternatively abut the hub210, interdigitate with the hub 210, and/or be otherwise coupled (e.g.,attached) to the hub 210 (e.g., by one or more elements of the matingmechanisms, such as an axial retention mechanism 310).

3.2.2 Blades.

The blades 220 are preferably statically connected to the hub 210, butcan additionally or alternatively be coupled to the hub 210 in any othersuitable manner. The blades 220 can be arranged radially outward of thehub axis 211. The blades 220 preferably each radiate out from the hub210, but alternatively the hub can surround the blades 220 (e.g.,surround circumferentially), can be coupled to the blades 220 alongtheir length (e.g., wherein the hub 210 defines ribs between the blades220), and/or have any other suitable arrangement.

In a first embodiment, the propeller 200 can operate with highefficiency and/or at a low Reynolds number. In this embodiment, thepropeller 200 preferably enables low power consumption for aerial systemflight (e.g., in low altitude rotary wing drone applications). Thepropeller 200 can include a plurality of blades 220, with evenly orun-evenly distributed angle separation between blades (e.g., about thehub axis 211). The blades 220 can optionally include one or moreproplets (e.g., upward, downward, bi-directional, etc.), preferablyarranged at or near the blade tip. The proplets preferably define aproplet height of 2%-6% of the propeller blade radius (e.g., distancefrom the hub cylinder axis to the outer propeller blade end). Thepropeller 200 of this embodiment typically works under 6.0×10³-1.0×10⁵Re flow condition, with power loading typically greater than 8 g/W(e.g., as shown in FIG. 11) and/or figure of merit typically above 65%.The blades 220 can optionally define a symmetric profile along some orall of a propeller blade central axis (e.g., within 20%-80% of thedistance along the length of the blade 220).

In this embodiment, for one or more points on the propeller bladecentral axis (e.g., for each point on the axis between an inner andouter propeller blade end), one or more of the blades 220 preferablydefine a chord on a propeller blade cross-section including the point,the chord defining a normalized chord length C_(r) substantially definedby the equation:

$C_{r} = {{a_{1} \times \left( {1 - \frac{r}{R}} \right)^{3}} + {3 \times a_{2} \times \left( \frac{r}{R} \right)*\left( {1 - \frac{r}{R}} \right)^{2}} + {3 \times a_{3} \times \left( \frac{r}{R} \right)^{2} \times \left( {1 - \frac{r}{R}} \right)} + {a_{4} \times \left( \frac{r}{R} \right)^{3}}}$and/or defining a twist angle β_(r) (e.g., angle between the chord and areference plane such as a plane normal the hub axis 211) substantiallydefined by the following equation:

$\beta_{r} = {{b_{1} \times \left( {1 - \frac{r}{R}} \right)^{3}} + {3 \times b_{2} \times \left( \frac{r}{R} \right)*\left( {1 - \frac{r}{R}} \right)^{2}} + {3 \times b_{3} \times \left( \frac{r}{R} \right)^{2} \times \left( {1 - \frac{r}{R}} \right)} + {b_{4} \times \left( \frac{r}{R} \right)^{3}}}$wherein r is a distance from the hub cylinder axis to the point and R isthe propeller blade radius. Preferably, a₁ is a constant greater than 8and less than 30, a₂ is a constant greater than 15 and less than 60, a₃is a constant greater than 15 and less than 60, a₄ is a constant greaterthan 5 and less than 25, b₁ is a constant greater than 40 and less than70, b₂ is a constant greater than 30 and less than 60, b₃ is a constantgreater than 15 and less than 40, and b₄ is a constant greater than 30and less than 70 (e.g., as shown in FIGS. 12A-12B).

In a first variation of this embodiment, the propeller diameter (e.g.,twice the distance from the hub axis 211 to a propeller blade tip) canbe 40-200 mm and a widest chord length can be 10-60 mm, preferablylocated 30%-50% of the distance along the length of the blade 220 (e.g.,measured from the axis of rotation). In one example of this variation,the propeller diameter is between 60 mm and 120 mm and the widest chordlength is between 10 mm and 60 mm. The point on the leading edge that isused to define the chord can be defined as the surface point of minimumradius, the surface point that will yield maximum chord length, or anyother suitable point. The blades 220 preferably define airfoils withlarge camber, small thickness, high lift coefficient, and highlift-to-drag ratio under low Reynolds number condition (e.g., as shownin FIG. 10B). The blades 220 can include sweep features (e.g., withinthe range of 75%-95% of the length of the blade from the hub axis 211),preferably with the magnitude of sweep smaller than 5% of the bladeradius (e.g., 2.5% of the propeller diameter).

The propeller 200 is preferably of unitary construction. Alternatively,the blades 220 can be inserted in to the hub 210 (e.g., retained withinthe hub by friction), otherwise fastened or affixed to the hub (e.g., bymechanical fasteners, by adhesive, etc.), and/or coupled to the hub inany other suitable manner. The propeller 200 can additionally oralternatively include any other suitable elements in any suitablearrangement.

3.3 Mating Mechanisms.

The mating mechanisms can function to couple the propeller 200 to therotor 120 and to align and/or retain the propeller 200 with respect tothe rotor 120. The aerial system 1 preferably includes one or moremating mechanisms, and each of the mating mechanisms can preferablyretain and/or align the propeller 200 and rotor 120 along one or moredirections. The directions can include an axial translation direction(e.g., directed substantially along the rotor axis 123 and/or hub axis211), a yaw direction (e.g., rotation about the axial translationdirection), radial translation directions (e.g., directed perpendicularto the axial translation direction), radial rotation directions (e.g.,rotations about axes perpendicular to the axial translation direction),and/or any other suitable directions. Each mating mechanism preferablyincludes complementary elements on (e.g., of unitary construction with,affixed to, etc.) each of the rotor 120 and hub 210, but canalternatively include only elements on one of the rotor 120 and hub 210,elements separate from both the rotor and hub, and/or elements in anyother suitable arrangement.

3.3.1 Axial Retention Mechanism.

The axial retention mechanism 310 functions to retain the hub 210 at therotor 120 in the axial translation direction, and can optionally retainthe hub in one or more other directions. The axial retention mechanism310 can fix the relative positions of the hub and rotor along the axis(e.g., rotor axis, hub axis), can limit the hub and rotor to a range ofrelative positions (e.g., wherein the hub and rotor are free totranslate with respect to each other within the range but are restrictedfrom exiting the range), or axially retain the hub and rotor in anyother suitable manner. The axial retention mechanism 310 preferablyretains the rotor within the void of the hub (e.g., as described above),but can additionally or alternatively retain the hub within a void ofthe rotor, or retain the hub and rotor in any other suitablearrangement.

The axial retention mechanism 310 is preferably configured to engage(thereby retaining the hub and rotor axially) in response to applicationof an insertion force (e.g., inward axial force) above a threshold value(e.g., 5 N, 8 N, 10 N, 12 N, 15 N, 20 N, 25 N, 30 N, 15-20 N, etc.). Theaxial retention mechanism 310 is preferably configured to disengage(thereby no longer retaining the hub and rotor axially) in response toapplication of a removal force (e.g., outward axial force) above athreshold value (e.g., 10 N, 15 N, 20 N, 25 N, 30 N, 35 N, 40 N, 25-35N, etc.). However, the axial retention mechanism 310 can operate usingany suitable insertion and/or removal force thresholds, and/or engage inresponse to application of any other suitable force applied in any othersuitable manner (e.g., torque).

The axial retention mechanism 310 preferably includes a first and secondaxial retention element (or a first and second set of axial retentionelements). One of the first and second axial retention elements ispreferably on the hub, and the other is preferably on the rotor. Thefirst and second axial retention elements are preferably complementary(e.g., wherein they cooperatively retain the hub and rotor axially). Forexample, the first and second axial retention elements can be configuredto fit together (e.g., abut, interdigitate, one retained within theother, etc.). However, the first and second axial retention elements canbe non-complementary or otherwise configured.

The axial retention mechanism 310 preferably includes a snap-fitretention mechanism, but can additionally or alternatively include alatch mechanism, friction fit mount, interference fit, bayonet mount,threaded mount, magnetic mechanism, and/or any other suitable retentionmechanism. The snap-fit retention mechanism preferably includes aprotrusion 311 (e.g., as the first axial retention element) and acomplementary recess 312 (e.g., as the second axial retention element),and can additionally or alternatively include any other suitableelements.

The protrusion 311 is preferably fixed to one of the hub or the rotor(captive element), but can alternatively be fixed to the stator or toany other suitable component. The protrusion 311 defines a protrusiondepth 317 (e.g., protrusion height) by which it protrudes from thecaptive element. The recess 312 is preferably fixed to the other of thehub or the rotor (i.e. capturing element; the element to which theprotrusion is not fixed). The recess 312 is preferably complementary tothe protrusion 311 (e.g., configured to fit around the protrusion). Whenthe axial retention mechanism 310 is engaged, the protrusion 311 ispreferably retained within the recess 312, and when the axial retentionmechanism 310 is not engaged, the protrusion 311 is preferably notwithin the recess 312.

The capturing element preferably includes additional elements arrangednear the recess 312 such that the protrusion 311 interacts with one ormore of the additional elements during engagement and/or disengagement.The additional elements can include a retention flange 313 (e.g., flangeincluding a wall of the recess), which can define a retention angle 316(e.g., between an axis such as the hub axis 211 and a tangent plane,such as a plane tangent to the wall at a point at which the protrusion311 contacts it during retention and/or removal). The additionalelements can include a lead-in surface 314 (e.g., a second wall of theretention flange, opposing the wall shared by the retention flange andthe recess), which can define an insertion angle 315 (e.g., between anaxis such as the hub axis 211 and a tangent plane of the lead-in surface314, such as a plane tangent to the lead-in surface 314 at a point atwhich the protrusion 311 contacts it during insertion). The insertionangle 315 can be 10°, 20°, 25°, 30°, 35°, 40°, 50°, 60°, 25°-35°,20°-40°, 10°-50°, less than 10°, greater than 50°, or any other suitableangle. The retention angle 316 can be 10°, 20°, 30°, 35°, 40°, 45°, 50°,55°, 60°, 65°, 70°, 80°, 90°, 40°-50°, 35°-55°, 30°-60°, less than 30°,greater than 60°, or any other suitable angle. During insertion and/orremoval, the rotor strain and/or hub strain is preferably less than athreshold value (e.g., 5%, 4%, 3%, 2.5%, 2%, 1.5%, etc.), and thefriction coefficient between the axial retention mechanism elements ispreferably within a target range (e.g., 0.45-0.55, 0.4-0.6, 0.3-0.7,0.1-1.0, etc.). The axial retention mechanism 310 (and/or any othersuitable element of the system) can additionally or alternativelyinclude one or more strain-relief elements 318 (e.g., notches, flexiblemembers, etc.). The strain-relief elements 318 can function to reducethe mechanical strain needed during mating and/or unmating, can allowregions of an element to strain (e.g., during mating and/or unmating)while other (e.g., adjacent) regions remain unstrained or less strained,and/or can function in any other suitable manner.

In a first example, the rotor is the outer element and the hub is theinner element. In this example, a cylindrical segment of the hub fitswithin a cylindrical void of the rotor, the hub includes an annularprotrusion, and the rotor includes a complementary recess, retentionflange, and lead-in surface.

In a second example (e.g., as shown in FIGS. 5A-5B), the rotor is theinner element and includes a cylindrical segment that fits within acylindrical void of the hub, which is the outer element. The rotorincludes an annular (e.g., circumferential) protrusion 311, preferablydefining a curved profile but additionally or alternatively defining anangular profile and/or other suitable profile. The hub defines acomplementary (e.g., annular, circumferential) recess 312. The recess312 is preferably arranged near an open end of the hub (e.g., wherein,when the hub and rotor are in the mated configuration, the rotor secondend 122 is near the open end of the hub). The retention flange 313(e.g., annular retention flange, circumferential retention flange,retention flange following substantially the same path as the recess312, etc.) is preferably arranged between the open end and the recess312 (e.g., in the mated configuration, arranged between the second end122 and the recess 312). The retention flange 313 can define an innerdiameter equal to, less than, or greater than the hub inner diameter212. The lead-in surface 314 is preferably arranged between the open endand the retention flange 313 (e.g., in the mated configuration, arrangedbetween the second end 122 and the retention flange 313). The lead-insurface 314 can be defined by a chamfer, bevel, round, and/or any othersuitable feature.

The elements of the axial retention mechanism (e.g., in the first andsecond examples) can be defined along the entire cylinder circumference,defined along portions of the circumference, and/or defined along anyother suitable paths and/or in any other suitable regions. Thecomplementary elements (e.g., protrusion 311, recess 312, retentionflange 313, lead-in surface 314, etc.) can be defined in substantiallythe same regions and/or in different regions (e.g., one element definedin only a subset of the regions of another element, elements having bothoverlapping and non-overlapping regions, etc.). The regions ofdefinition along the circumference can be unequally or equallydistributed (e.g., a number of regions, such as 2, 3, 4, 5, 6, or 7 ormore regions, regularly or irregularly spaced around the circumference),can be of equal or unequal sizes (e.g., each covering an angular segmentsuch as 5°, 10°, 15°, 20°, 30°, 40°, 2-10°, 10-20°, 20-40°, etc.) andcan be in a common or different plane (e.g., have offset locations alongthe hub axis). For example, the protrusion 311 can be defined along theentire circumference, and the retention flange 313 and lead-in surface314 can be defined only in a subset of the circumference (e.g., as shownin FIG. 16). The axial retention mechanism can optionally includestrain-relief elements 318. Examples of strain-relief elements 318 thatcan be used include: notches, springs, strain conversion mechanisms(e.g., that convert the strain to heat), interleaved flexible material,and/or any other suitable strain-relief element. In a specific example(e.g., as shown in FIGS. 17 and 18A-18C), a subset of regions of thepropeller 200 and/or motor 100 (e.g., the regions in which all elementsof the axial retention mechanism 310 are defined) can includestrain-relief elements 318 (e.g., notches), which can allow the subsetof regions to strain (e.g., during mating and/or unmating) whilereducing the strain in other regions.

However, the axial retention mechanism 310 can additionally oralternatively include any other suitable elements in any other suitablearrangement.

3.3.2 Rotational Retention Mechanism.

The rotational retention mechanism 320 functions to retain the hub 210at the rotor 120 in the yaw direction, and can optionally retain the hubin one or more other directions. The rotational retention mechanism 320can fix the relative positions of the hub and rotor about the axis, canlimit the hub and rotor to a range of relative positions (e.g., whereinthe hub and rotor are free to rotate with respect to each other withinthe range but are restricted from exiting the range), or retain the huband rotor about the axis in any other suitable manner.

The rotational retention mechanism 320 preferably includes a first andsecond rotational retention element or a first and second set ofrotational retention elements. The elements of the first and second setscan have a one-to-one relationship, a many-to-one relationship (e.g.,the first set can include two elements for each element of the secondset, one element of the first set arranged on each of two opposing sidesof each element of the second set), or any other suitable relationship.One of the first and second rotational retention elements is preferablyon the hub, and the other is preferably on the rotor. The first andsecond rotational retention elements are preferably complementary (e.g.,wherein they cooperatively retain the hub and rotor in the yawdirection). For example, the first and second rotational retentionelements can be configured to fit together (e.g., abut, interdigitate,one retained within the other, etc.). However, the rotational retentionelements can be otherwise arranged and configured. The first and secondrotational retention elements can contact at a surface defining a normalvector, preferably wherein the inner product of the normal vector and arotation tangent vector (e.g., tangent to the yaw direction at a pointradially aligned with the contact surface) is substantially non-zero,more preferably wherein the normal and tangent vectors are substantiallyparallel (e.g., defining an angle less than a threshold angle, such as1°, 3°, 10°, etc.).

In a first variation, the rotational retention mechanism 320 includes atleast one radial member 321 fixed to one of the hub or rotor, and atleast one limit member 322 (e.g., member extending substantiallyparallel the rotor axis 123 and/or hub axis 211) fixed to the other ofthe hub or rotor. The limit member 322 can be configured to contact theradial member 321 (e.g., thereby preventing rotation of the radialmember past the limit member). The radial members can radiate inwardand/or outward (e.g., from a body or void, such as a cylindrical body orvoid; from a central member; from an axial retention element, etc.).

In a first example of this variation, the rotor 120 includes a pluralityof ribs (radial members 321) extending radially inward from the rotorcylinder, preferably meeting at or near the rotor axis 123, and the hub210 includes a plurality of limit members 322 (e.g., extending upwardand/or downward from one or more radial ribs of the hub) arranged onboth sides of each radial member 321 (e.g., as shown in FIGS. 7B-7C). Ina specific example, the rotor and hub each include three radial ribsarranged with equal angular spacing about the rotor and hub axes,respectively, and the hub includes six limit members (two for eachradial rib of the rotor).

In a second example, the hub includes protrusions (e.g., bosses, pins,dowels, etc.), preferably protruding substantially parallel the hub axis211 but alternatively at any suitable angle to the hub axis 211, thatalign with complementary holes defined in the rotor (e.g., in the rotorcylinder, in one or more radial members of the rotor, etc.).

In a third example, the annular recess and protrusion of the axialretention mechanism 310 vary along their length (e.g., based on angularposition). In a specific example, the recess and protrusion are onlydefined in some angular sections, and are absent from others (e.g., donot extend around the entire circumference of the cylindrical bodies).However, the rotational retention mechanism 320 can additionally oralternatively include any other suitable elements arranged in any othersuitable manner.

3.3.3 Radial Alignment Mechanism.

The radial alignment mechanism 330 can function to retain the hub 210 atthe rotor 120 in the radial translation and rotation directions, and canoptionally retain the hub in one or more other directions. The radialalignment mechanism 330 preferably fixes the relative positions of thehub and rotor in the radial translation and rotation directions, but canalternatively limit the hub and rotor to a range of relative positions(e.g., wherein the hub and rotor are free to move in the radialtranslation and/or rotation directions with respect to each other withinthe range but are restricted from exiting the range) or retain the huband rotor about the axis in any other suitable manner. The radialalignment mechanism 330 preferably establishes and/or maintains asubstantially coaxial alignment of the rotor axis 123 and hub axis 211(e.g., establishing and/or maintaining parallelism and/or concentricityof cylindrical bodies defined by the rotor 120 and hub 210), but canadditionally or alternatively establish and/or maintain any othersuitable alignments.

The radial alignment mechanism 330 preferably includes a first andsecond radial alignment element (or a first and second set of radialalignment elements). One of the first and second radial alignmentelements is preferably on the hub, and the other is preferably on therotor. The first and second radial alignment elements are preferablycomplementary. For example, the first and second radial alignmentelements can be configured to fit together (e.g., abut, interdigitate,one retained within the other, etc.). However, a radial alignmentmechanism pair can be otherwise configured. The system can include oneor more radial alignment mechanism pairs, which can be evenly arcuatelyand/or radially distributed or otherwise configured.

In a first variation, an axial protrusion 331 (e.g., boss, dowel, pin,shaft, etc.) on one of the hub or rotor is configured to fit into a hole332 (e.g., pocket, through-hole, etc.) in the other of the hub or rotor(e.g., as shown in FIG. 6). The axial protrusion 331 is preferably onthe rotor and the hole 332 is preferably in the hub, but alternativelythe axial protrusion 331 can be on the hub and the hole 332 can be inthe rotor. The axial protrusion 331 and hole 332 are preferably circularand centered on the rotor axis 123 and/or hub axis 211. Alternatively,the axial protrusion 331 and/or hole 332 can be non-circular, the radialalignment mechanism 330 can include more than one axial protrusion 331and/or hole 332, and/or the axial protrusion(s) 331 and hole(s) 332 canbe arranged off-axis (e.g., with a rotationally symmetric or asymmetricdistribution), which can enable the axial protrusion 331 and hole 332 toadditionally function as a rotational retention mechanism 320. The axialprotrusion 331 and hole 332 preferably have a clearance fit, but canalternatively have an interference fit, a snap fit, and/or any othersuitable fit. The axial protrusion 331 and/or hole 332 can includefeatures (e.g., chamfers, fillets, rounds, etc.) to help guide them intoalignment (e.g., during mating of the hub and rotor). In a specificexample, the hole 332 is defined in a central segment of the hub 210 anda boss (axial protrusion 331) is defined at the center of the rotor,each defined where a plurality of radial ribs (e.g., of the rotationalretention mechanism 320) meet. The interior surface of the hole and/orexterior surface of the boss can optionally define chamfers, rounds,and/or any other suitable lead-in features. In a second variation, oneof the hub or rotor includes a pair of axial protrusions (e.g., fins)and the other of the hub or rotor includes a rib (e.g., radial rib),wherein the axial protrusions are separated by a distance substantiallyequal to or slightly larger than the rib width. However, the radialalignment mechanism 330 can include any other suitable elements in anyother suitable arrangement.

3.3.4 Damping Mechanism.

The damping mechanism 340 can function to reduce vibration transmissionbetween the hub and rotor, and can optionally retain the hub and rotorwith respect to each other (e.g., function as one or more of theretention and/or alignment mechanisms). The damping mechanism 340 can bearranged between the hub and rotor, preferably compressed between them(e.g., having an interference fit). The damping mechanism 340 ispreferably affixed to and/or embedded in (e.g., glued to, retainedwithin a groove of, etc.) one of the hub or rotor, but can alternativelybe retained only by the interference fit and/or retained in any othersuitable manner.

The damping mechanism 340 preferably includes (e.g., is made of) one ormore flexible materials (e.g., rubber, silicone, etc.), but canadditionally or alternatively include rigid materials and/or any othersuitable materials. The damping mechanism 340 can define shapes such asdots, lines, and/or pads. The damping mechanism 340 can include one ormore damping elements. The elements can be arranged circumferentially(e.g., around an entire circumference, around a portion of acircumference), axially (e.g., parallel the rotor axis 123 and/or hubaxis 211), diagonally, and/or in any other suitable directions.

In a first example, the damping mechanism 340 includes an O-ringretained in a groove of the inner element (e.g., as shown in FIGS.9A-9B). The O-ring can be arranged axially above or below the axialretention mechanism interface. Additionally or alternatively, the O-ringcan optionally function as an axial retention mechanism 310 and/orrotational retention mechanism 320. In a second example, the dampingmechanism 340 includes a plurality of axial ribs with equal angularspacing around the outside of the inner element and/or the inside of theouter element. However, the damping mechanism 340 can additionally oralternatively include any other suitable elements in any other suitablearrangement.

3.3.5 Additional Elements.

The mating mechanisms can additionally or alternatively includefasteners (e.g., screws, latches, etc.). For example, the matingmechanisms can include self-locking low cap screws, threaded holes, andcounterbored through-holes (e.g., as shown in FIGS. 8A-8B), which canfunction as secure and/or low-profile fasteners.

The mating mechanisms can additionally or alternatively include one ormore grip-enhancing elements. The grip-enhancing elements can functionto allow and/or facilitate manual gripping of the motor 100 and/orpropeller 200 (e.g., to mate or unmate the hub 210 from the rotor 120).In a first variant, the propeller blades 220 can function asgrip-enhancing elements. In a second variant, the grip-enhancingelements can include grooves defined in an outer surface of the hub.However, the mating mechanisms can additionally or alternatively includeany other suitable elements in any other suitable arrangement.

4. Method.

A method 400 for aerial system use can include mating a motor andpropeller S410, rotating the propeller S420, ceasing propeller rotationS430, and/or unmating the motor and propeller S440 (e.g., as shown inFIG. 13). The method 400 is preferably performed using the aerial system1 and/or propulsion assembly 2 described above, but can additionally oralternatively be performed using any other suitable aerial system.

Mating the motor and propeller S410 can include establishing alignmentsbetween the rotor and hub (e.g., approximate alignments, precisealignments, etc.), which can include coaxial alignment (e.g., in theradial translation and/or rotation directions) and/or rotationalalignment (e.g., in the yaw direction), and applying inward axial force(e.g., greater than an insertion force threshold). Elements of thesystem (e.g., mating mechanisms) can guide the mating of the hub to therotor (e.g., guiding from approximate alignment into more precisealignment) and subsequently maintain the desired arrangement.

A specific example of mating the motor and propeller S410 includes:establishing approximate coaxial alignment between the propeller and therotor (e.g., manually, such as by holding the propeller in one hand andthe motor or aerial system housing in the other hand); establishingapproximate yaw alignment between the propeller hub and the rotor (e.g.,aligning the radial ribs of the hub and rotor), so that the chamferingof the limit members will cause the rotor ribs to align more preciselyduring mating; and pressing the propeller toward the rotor along theaxial direction. In this specific example, if the propeller and themotor are not approximately aligned, the propeller hub cylinder willcontact the top surface of the motor housing so that the propeller hubcannot be pressed into the mating configuration. In this specificexample, when axial pressure is applied, the annular protrusion passesover the retention flange and the inner surface of the hub contacts thetop surface of the motor housing. During this process, an audible soundis preferably emitted, which can indicate that the installation iscomplete. However, the motor and propeller can be otherwise mated.

Rotating the propeller S420 is preferably performed by the motor, andcan function to propel the aerial system and/or to control aerial systemflight. Rotation of the rotor preferably causes the propeller to rotate(e.g., due to the rotational retention mechanism). During propellerrotation, the force generated by the propeller (e.g., reaction forcecaused by air displaced by the propeller) preferably retains thepropeller against the hub axially (e.g., the force is directedsubstantially along the axis in the inward or mating direction). In aspecific example, in which the propeller is mounted to the rotor frombelow, when the propeller is driven by the motor, the propellergenerates a propulsion force, so that the inner surface of the propellerhub and the top surface of the motor housing are retained against eachother (e.g., as shown in FIG. 14).

Ceasing propeller rotation S430 can function to cease aerial systemflight. Ceasing propeller rotation S430 is preferably performed by themotor (e.g., by ceasing motor rotation, by ceasing powered motorrotation, etc.).

Unmating the motor and propeller S440 preferably includes applyingoutward axial force (e.g., greater than a removal force threshold), morepreferably by holding the propeller (e.g., by a grip-enhancing element)in one hand, retaining the motor or aerial system housing (e.g., in asecond hand, in a stand, pressed against a surface, etc.), and pullingthe propeller away from the motor in the outward axial direction. In aspecific example, S440 includes orienting the aerial system so that thepropeller is above the motor, gently holding the propeller bladesbetween the fingers of a hand, and pulling upward to unmate thepropeller. S440 can be performed to remove a damaged propeller (e.g.,for subsequent replacement by a functional propeller), to remove a firsttype of propeller (e.g., for subsequent replacement by a second type ofpropeller), and/or for any other suitable purpose. However, the method400 can include any other suitable elements performed in any othersuitable manner.

Although omitted for conciseness, the preferred embodiments includeevery combination and permutation of the various system components andthe various method processes. Furthermore, various processes of thepreferred method can be embodied and/or implemented at least in part asa machine configured to receive a computer-readable medium storingcomputer-readable instructions. The instructions are preferably executedby computer-executable components preferably integrated with the system.The computer-readable medium can be stored on any suitable computerreadable media such as RAMs, ROMs, flash memory, EEPROMs, opticaldevices (CD or DVD), hard drives, floppy drives, or any suitable device.The computer-executable component is preferably a general or applicationspecific processing subsystem, but any suitable dedicated hardwaredevice or hardware/firmware combination device can additionally oralternatively execute the instructions.

The FIGURES illustrate the architecture, functionality and operation ofpossible implementations of systems, methods and computer programproducts according to preferred embodiments, example configurations, andvariations thereof. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, step, or portion of code,which comprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block can occurout of the order noted in the FIGURES. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:
 1. A system for an aerial vehicle, the system comprising: arotor defining a cylindrical body, the cylindrical body defining a firstand second end, a rotor cylinder axis, and a rotor diameter; a propellercomprising a hub and a propeller blade mechanically coupled to the hub,the hub defining a cylindrical void, the cylindrical void defining a hubcylinder axis and a hub inner diameter greater than the rotor diameter;a radial alignment mechanism mechanically coupled to the rotor proximalthe first end and to the hub, the radial alignment mechanism retainingthe hub cylinder axis substantially collinear with the rotor cylinderaxis, the radial alignment mechanism comprising: a first surfacedefining a hole substantially centered on the rotor cylinder axis; and aboss retained within the hole; a rotational retention mechanismmechanically coupled to the rotor proximal the first end and to the hub,the rotational retention mechanism rotationally retaining the hub aboutthe rotor axis with respect to the rotor, the rotational retentionmechanism comprising: a radial member extending radially inward of thecylindrical body; and a limit member contacting the radial member; andan axial retention mechanism mechanically coupled to the rotor proximalthe second end and to the hub, the axial retention mechanismtranslationally retaining the hub with respect to the rotor along anaxial direction parallel the rotor cylinder axis, the axial retentionmechanism comprising: a second surface defining a circumferentialrecess; and a circumferential protrusion defined along a third surfaceseparate from the second surface, the circumferential protrusionretained within the circumferential recess.
 2. The system of claim 1,wherein: the second surface is defined by the hub; the circumferentialprotrusion is attached to the rotor more proximal the second end thanthe first end; and a protrusion radius from the rotor cylinder axis tothe circumferential protrusion is greater than half the hub innerdiameter.
 3. The system of claim 2, wherein the axial retentionmechanism further comprises: a circumferential retention flange attachedto the second surface, the circumferential retention flange arrangedproximal the second end relative to the circumferential recess, whereina flange radius from the hub cylinder axis to the circumferentialretention flange is greater than the protrusion radius; and a lead-insurface attached to the circumferential retention flange, the lead-insurface arranged proximal the second end relative to the circumferentialretention flange, the lead-in surface defining a tangent plane at anoblique angle to the second end and to the hub cylinder axis.
 4. Thesystem of claim 1, wherein the hub inner diameter exceeds the rotordiameter by more than 1 mm.
 5. The system of claim 1, wherein: the hubcomprises a hub end proximal the second end, the hub end defining a hubend plane normal the hub cylinder axis; the hub end plane and the rotorcylinder axis intersect at an intersection point; and a distance fromthe intersection point to a region of the rotor within the hub isgreater than half the hub inner diameter.
 6. The system of claim 1,wherein the limit member extends substantially parallel the rotorcylinder axis.
 7. The system of claim 1, wherein: the radial membercomprises a first side and a second side opposing the first side, thefirst and second sides substantially parallel the rotor cylinder axis;the limit member contacts the first side; and the rotational retentionmechanism further comprises a second limit member contacting the secondside.
 8. The system of claim 1, wherein the radial member is attached tothe rotor and the limit member is attached to the hub.
 9. The system ofclaim 8, wherein the boss is attached to the radial member and the firstsurface is mechanically coupled to the hub.
 10. The system of claim 1,further comprising a damper arranged between the rotor and the hub. 11.The system of claim 10, wherein the damper comprises a gasket arrangedcircumferentially around the rotor.